Hello,
I am currently working on modeling a high temperature hydrogen heat exchanger. I decided to start as simple as possible and just model the heat transfer into an axi-symmetric tube of hydrogen surrounded by a solid shell.
I am running into two problems. First, COMSOL has decided that the conservation of mass is a suggestion at best and need not be followed. As a check on the results I was getting, I checked the mass flow rate per unit area. I found that the exit mass flow rate is about 25% higher than the inlet mass flow rate. Thus something is obviously wrong with this.
Second, although I have experimented with treating the hydrogen as both a fluid and an ideal gas, at the moment I am letting it be an ideal gas. However, COMSOL doesn't seem the ideal gas law any more than it did the law of conservation of mass. When the pressure and temperature at the inlet are used in combination with the specific gas value of hydrogen (4124 j/kg), a rearranged ideal gas equation rho=P/(R*T) says that the density should be about 1.4 kg/m^3. COMSOL however, returns a value 17 thousand times less than that.
Does anyone have any thoughts or ideas on these problems?
Dan
I am currently working on modeling a high temperature hydrogen heat exchanger. I decided to start as simple as possible and just model the heat transfer into an axi-symmetric tube of hydrogen surrounded by a solid shell.
I am running into two problems. First, COMSOL has decided that the conservation of mass is a suggestion at best and need not be followed. As a check on the results I was getting, I checked the mass flow rate per unit area. I found that the exit mass flow rate is about 25% higher than the inlet mass flow rate. Thus something is obviously wrong with this.
Second, although I have experimented with treating the hydrogen as both a fluid and an ideal gas, at the moment I am letting it be an ideal gas. However, COMSOL doesn't seem the ideal gas law any more than it did the law of conservation of mass. When the pressure and temperature at the inlet are used in combination with the specific gas value of hydrogen (4124 j/kg), a rearranged ideal gas equation rho=P/(R*T) says that the density should be about 1.4 kg/m^3. COMSOL however, returns a value 17 thousand times less than that.
Does anyone have any thoughts or ideas on these problems?
Dan